It was recalled that, because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors doped with rare-earth elements had attracted attention since a high Curie temperature was obtained in rare-earth-doped GaN dilute magnetic semiconductors and a colossal magnetic moment was observed in Gd-doped GaN thin film. GaN dilute magnetic semiconductors doped with rare-earth elements (La, Ce-Yb) were systemically studied by using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. The electronic structures of dilute magnetic semiconductors were studied; especially with regard to the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. It was found that, for materials containing f electrons, electronic correlation was usually strong and the spin-orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm were stabilized at antiferromagnetic phase, while GaN doped by other rare-earth elements showed strong ferromagnetism which was suitable materials for spintronic devices. Moreover, it was noticed that the observed large enhancement of magnetic moment in GaN was mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the rare-earth doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of rare-earth-doped semiconductors in the third generation high efficiency photovoltaic devices.

Ga Vacancy Induced Ferromagnetism Enhancement and Electronic Structures of RE-Doped GaN. G.Zhong, K.Zhang, F.He, X.Ma, L.Lu, Z.Liu, C.Yang: Physica B, 2012, 407[18], 3818-27